Many people suffer from various forms of neural cell damage or impaired neural cell function. Clinical conditions associated with neural cell damage or impaired neural cell function include, but are not limited to, retinal damage (such as retinitis pigmentosa, retinal detachment, diabetic retinopathy, and macular degeneration), optic neuropathy, glaucoma, stroke, spinal cord injury, peripheral nerve injury, demylinating disease (such as multiple sclerosis), and central nervous system injury secondary to ischemia, compression, injury, infection, elevated incranial pressure, congenital and hereditary genetic disease, metabolic derangement, tumors, toxic neuropathy and encephalopathy, lysosomal storage diseases, mitochondrial diseases, neurological sequelae of systemic diseases such as chronic arterial hypertension, diabetes, HIV infection, systemic lupus, coagulation disorders, Parkinsons disease, Alzheimers disease, and prion disease. Retinal damage or impaired retinal function can lead to diminished sight and blindness. And, as the age of the general population increases, the number of people suffering from diminished sight due to these causes increases.
Since many cells such as neurons, including retina, are stimulated via electrical signals, it has also been known that functions of these cells can be restored by providing an appropriate electrical stimulation. In fact, several devices have been developed to attempt to restore vision loss due to retinal damage. For example, photovoltaic devices, which are attached to a portion of a retina, have been developed to stimulate rods and cones within the retina. Although such devices may provide some stimulation, the devices suffer from several drawbacks. In particular, the devices are relatively large (e.g., on the order of square millimeters). As a result, when placed on a retina, the devices block significant portions of light that would otherwise reach rods and cones located behind the devices. Another problem associated with these devices is that they are placed on a surface of the retina, which is delicate; thus, the retina surface may tear or otherwise become damaged when the devices are attached to the retina.
Other silicon-chip based devices that are implanted sub-retinally have also been developed to attempt to improve vision in those suffering from retinal damage. Mild improvement of electrical response to light has been observed using these devices. However, several problems have also been observed. Specifically, because the devices are relatively large, once the devices are attached to the retina, oxygen is blocked from reaching cells adjacent to or proximate the devices. In addition, implantation of the devices is thought to further damage the retinal tissue.
Accordingly, there is a need for a method for electrically stimulating cells using a significantly smaller device and without causing further damage to the cells.